Odd Lot and Round Lot
A round lot is the standard trading unit for a stock, traditionally 100 shares or a multiple of 100. An odd lot is an order for fewer than 100 shares. The US has updated round-lot definitions so higher-priced stocks use smaller round lots.
Stock markets were built around blocks of 100 shares. Orders of that size — round lots — set the official quotes, while smaller "odd lots" were treated as second-class. With share prices in the hundreds or thousands of dollars and fractional investing, that old split no longer fits, and US rules are changing. This entry explains both terms and why they still matter.
- Category
- Market Structure
- Reading time
- 4 min
- Also called
- Odd lot, Round lot, Odd-lot order
- Updated
Odd lots and round lots in plain words
A round lot is a trading order typically of 100 shares or a multiple of 100.1
An odd lot is a trading order for fewer than 100 shares.2
The SEC has accelerated new round-lot definitions and requirements to show the best-priced odd-lot orders in market data.3
How lot sizes affect trading, step by step
Check your order size
Under 100 shares is usually an odd lot. See Lot Size.
Know the quote
Official best quotes historically came from round lots. See National Best Bid and Offer.
Odd lots can be better priced
Smaller orders sometimes sit inside the quoted spread.
Watch high-priced stocks
Most orders in pricey shares are odd lots.
Fractional shares
Below one share entirely. See Fractional Shares.
Check your broker
Handling of odd lots can differ.
Worked examples
Example 1 — Classifying orders
Mixed orderOrders for 300, 75 and 150 shares.
| 300 shares | Round lot (3 × 100) |
| 75 shares | Odd lot |
| 150 shares | Round lot + 50-share odd lot |
Round lots are 100 shares or multiples; anything under 100 is an odd lot.1
Example 2 — The cost of a round lot
Odd lots dominateA stock trades at $800.
| 100-share round lot | 100 × $800 = $80,000 |
| 10-share odd lot | 10 × $800 = $8,000 |
For expensive stocks, a 100-share lot is so large that most retail orders are odd lots. See Fractional Shares.
Example 3 — Hidden better price
Better priceThe official quote is $50.00 / $50.05, but a 30-share odd lot offers at $50.02.
| Round-lot ask | $50.05 |
| Odd-lot ask | $50.02 |
| Saving on 30 shares | 30 × $0.03 = $0.90 |
New rules require market data to identify the best-priced odd-lot orders available.3
Odd lot vs round lot
| Aspect | Odd lot | Round lot |
|---|---|---|
| Size | Fewer than 100 shares | 100 shares or a multiple |
| Official quote | Historically excluded | Sets the NBBO |
| Typical trader | Retail | Institutions, market makers |
| Rule changes | Odd-lot data being published | Smaller lots for pricey stocks |
Where lot sizes matter
Reading quotes
Understanding what the NBBO includes. See National Best Bid and Offer.
Order routing
How brokers handle small orders. See Smart Order Routing.
Options
One contract usually covers 100 shares. See Options.
Forex
Lot sizes there mean something different. See Lot Size.
Advantages and disadvantages
Advantages
- Odd lots let small investors buy any number of shares.
- Round lots standardise quoting.
- Reforms improve price transparency.
Disadvantages
- Odd-lot prices were long invisible in official quotes.
- 100-share lots are outdated for expensive stocks.
- Terminology differs between markets.
Going deeper
Read as far as you need. Each level builds on the one before it.
Not just stocks
Beginner
The idea of a standard unit appears everywhere — options contracts, futures and forex lots — but the sizes differ by market. See Lot Size.
Delayed reforms
Intermediate
The new round-lot and odd-lot definitions were approved in 2020, but their implementation was delayed until the SEC accelerated it in 2024.3
Compliance dates
Advanced
The SEC set the round-lot compliance date for November 2025 and odd-lot information for May 2026.3
Common mistakes
Thinking odd lots are penalised
Most brokers now treat them like other orders.
Ignoring odd-lot prices
They can be better than the official quote.
Mixing up forex lots
A forex standard lot is 100,000 units of currency.
Assuming 100 shares everywhere
Round-lot sizes now vary with price in the US.
Check your understanding
Test yourself before moving on. Each answer comes with an explanation.
Key points to remember
- A round lot is traditionally 100 shares or a multiple.
- An odd lot is fewer than 100 shares.
- Odd lots were long left out of official quotes.
- US rules now shrink round lots for pricey stocks.
- Odd-lot best prices are being published.
Frequently asked questions
Can I buy fewer than 100 shares?
Why 100 shares?
Do odd lots get worse prices?
Further learning
- Lot Size
Lot sizes across markets.
- National Best Bid and Offer
The official best quote.
- Block Trade
The other end of the size scale.
Sources
This article is written in our own words. The sources below support the specific facts, rules and figures marked with a number in the text. Links open the original publisher’s page.
- Nasdaq. Round lot (glossary) (opens in a new tab) Checked .
- Nasdaq. Odd lot (glossary) (opens in a new tab) Checked .
- U.S. SEC. SEC Adopts Rules to Amend Minimum Pricing Increments and Access Fee Caps (round lot definitions) (opens in a new tab) Checked .
Educational content, not financial advice. Examples use hypothetical prices and simplified costs; actual fees, margin rules and regulations vary by broker, market and country. We are not affiliated with any publisher linked above. Last reviewed . Report an error or request a source credit.